Art of making leatherboard



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beaten UUHI PATENT QFFECE ART OF MAKING LEATHERBOARD Herman W. Richter,Bridgewater, Mass, assignor to George 0. Jenkins Company, Bridgewater,Mass, a corporation of Massachusetts No Drawing. Application March 29,1935, Serial No. 13,669

9 Claims.

This invention relates to the art of making light colored leatherboard.In certain of its aspects the invention is in the nature of animprovement on the invention disclosed in Patent No. 1,975,556 issued tome on October 2, 1934.

As explained in my prior patent, leatherboard, which is often termedheeling board, is a material made from a furnish composed principally ofleather scrap or waste (sole leather cuttings,

skivings, etc.) by board making processes, which involve disintegrationin a beating engine and subsequent formation into sheets or slabs on aWet machine. Leatherboard manufactured by this process is of a ratherdark, unattractive hue, due undoubtedly to the presence of iron-tannateinks formed in the leatherboard during its fabrication by chemicalreaction between the tannins present in the leather scrap and the ironof the fabricating apparatus.

My prior invention depended upon the fact that the iron-tannate inks orsaddening material can be destroyed or eliminated by the application ofvery dilute solutions of bleaching agents, so as to liberate the naturalcolor of the leather fiber, without injuriously affecting its durabilityor other desirable qualities. In my previous patent I have mentioned anumber of suitable acid reducing reagents which can be used to liberatethe natural color of the leather fiber. Of those mentioned oxalic acidhas been found to be most acceptable in commercial operation. Thecustomary mode of carrying out the process prior to the presentinvention consisted in dipping the board in a dilute aqueous solution ofoxalic acid of about 3% concentration. This concentration of bleachingagent results in a palecolored product that takes the usual light stainsand dressings without the undesirable darkening or discoloration socharacteristic of untreated leatherboard. A 2% solution does not produceso pale a board and a 4% concentration throws the shade more on thereddish side, which is not as desirable as a pale color. Furthermore, aconcentration in excess of 3% appears to impair to a certain extent someof the desirable qualities of the leather fiber, particularly itsflexibility. Hence, in the process as commercially practiced under myprior patent it was always considered necessary to maintain a carefulcontrol to insure the desired change in color of the product and toavoid a harmful excess in concentration.

It is the primary object of the present invention to modify the processdisclosed in my prior patent in such a manner as to reduce to a minimumor to obviate entirely the necessity for carefully controlling theconditions under which the process is practiced.

Another object is to modify the process of my prior patent in such amanner as to reduce to a minimum the amount of chemical necessary toproduce a desired eifect.

Another object is to provide a simple and economical method forbleaching sheet material containing leather fiber.

The invention is based upon the discovery or observation that solublebinoxalates have a far greater bleaching action on saddening materialspresent in leatherboard than has oxalic acid. 'For instance, a 1.75%aqueous solution of an alkali binoxalate such as potassium binoxalate(salt of sorrel) appears to have substantially the same bleaching eifectas that produced by a 3% oxalic acid solution. Since a 3% solution ofoxalic acid contains 2.14 grams anhydrous oxalic acid per grams ofsolution and a 1.75% solution of potassium binoxalate contains .54 gram,.575 gram or .615 gram of anhydrous oxalic acid per 100 grams ofsolution (depending upon the number of molecules of water ofcrystallization), it is obvious that the use of the acid salt instead ofthe acid itself results in a considerable economy. A 1.75% solution ofbinoxalate contains less anhydrous oxalic acid than a 1% solution ofoxalic acid, yet it produces a bleaching effect substantially equal tothat produced by a 3% oxalic acid solution.

It is to be noted that the binoxalates are considerably less soluble inwater than oxalic acid. Oxalic acid is soluble to the extent of 10%while both sodium and potassium binoxalate are soluble only to theextent of about 2%. It, therefore, follows that by using a solublebinoxalate instead of oxalic acid, the necessity for a careful controlof the process is reduced to a minimum or obviated entirely. For, it isno longer possible to introduce into the leatherboard sufiicient oxalicacid to produce a reddish board or to injuriously affect theleatherboard fiber.

The bleaching agent may be applied to the material to be treated invarious ways. I prefer to dip the finished sheet of leatherboard into a1.75% solution of potassium binoXalate (salt of sorrel) or sodiumbinoxalate until the desired bleaching effect is produced. If a uniformeffect throughout the board is desired, the board is left in thebleaching solution until complete penetration takes place. As in thecase of my prior patent, by arresting the process before completepenetration occurs, I can simulate the difference in shade which can beobserved between the grain surface and the center of any out section ofhide leather.

The foregoing constitutes the essential and distinctive thought of myinvention, but it is to be distinctly understood that the same may becombined with various details and expedients without materiallyaffecting the peculiar results obtained and that changes andmodifications may be resorted to without departing from the spirit ofthe invention or the scope of the appended claims, in which I intend toclaim all the patentable novelty inherent in my invention.

I claim:

1. The method of bleaching leatherboard which consists in treating theleatherboard with an aqueous solution of an alkali binoxalate.

2. The method of bleaching leatherboard which consists in treating theleatherboard with an aqueous solution of potassium binoxalate.

3. The method of bleaching leatherboard which consists in treating theleatherboard with an aqueous solution of potassium binoxalate, theconcentration of the solution being approximately 1.75%.

4. The method of bleaching leatherboard which consists in dipping theleatherboard into an aqueous solution of an alkali binoxalate.

5. The method of bleaching leatherboard which consists in dipping theleatherboard into an aqueous solution of potassium binoxalate.

6. The method of bleaching leatherboard which consists in dipping theleatherboard into an aqueous solution of potassium binoxalate, theconcentration of the solution being approximately 1.75%

7. The method of making a sheet of leatherboard having substantially thesame difference in shade between its grain surface and center as has acut section of hide leather, which method consists in subjecting a sheetof leatherboard to the bleaching action of an aqueous solution of analkali binoxalate for a period of time insufficient to permit completepenetration of the solution.

8. The method of making a sheet of leatherboard having substantially thesame difference in shade between its grain surface and center as has acut section of hide leather, which method consists in subjecting a sheetof leatherboard to the bleaching action of an aqueous solution ofpotassium binoxalate for a period of time insufficient to permitcomplete penetration of the solution.

9. A method for bleaching a sheet material containing leather fiberwhich consists in subjecting the material to the action of an aqueoussolution of potassium binoxalate.

HERMAN W. RICHTER.

